1. Field of the Invention
The present invention relates generally to the field of vehicles, and particularly to vehicle drive trains.
2. Description of the Related Art
Airlines use push-back tractors to move aircraft around at airports. Such tractors need to operate at low speed and high torque in order to move aircraft. However, when the tractors uncouple from the aircraft, it is important for them to be able to get back to the gate area as fast as possible, which requires operating at high speed and low torque. Tractors, and other vehicles powered by internal combustion engines, employ multi-speed gear boxes that enable an operator to deal with this two-mode operation simply by shifting gears. However, this two-mode operation remains a problem for vehicles having electric power trains because a typical gear box configuration for an electric power train application is a single speed (i.e., gear ratio) without a clutch or a gear shift.